The present invention is directed to a motor-operated hand-held device, such as a drilling device, including a housing with a rotary spindle located in the housing and projecting out of it for transmitting rotational movement from a driving motor to a tool secured to the rotary spindle. A safety device is provided for preventing deflection of the housing of the hand-held device about the axis of the rotary spindle if the tool suddenly becomes locked or jammed. The safety device can be activated by a detection device in the event the tool becomes jammed.
Hand held devices of the generic type such as drilling devices or cutting and grinding devices are used primarily by professional craftsmen but also to an increasing degree by nonprofessionals for home use. Operation of such hand-held devices entails the risk that the tool held in the rotary spindle will become jammed as the result of improper operation on the part of the operator or user or, for example, when striking reinforcing steel while drilling holes in reinforced concrete. The sudden locking of the rotary spindle causes high reaction torques which lead to a deflection of the housing about the rotary spindle axis. Normally the tool operator is unprepared for such a reaction and is taken by surprise by the deflection of the hand held device and may lose his grip on the device, or, when working at elevated positions, such as on scaffolds and ladders, can lose his balance and fall which could result in injury.
To avoid such situations, in the past various steps have been proposed using the principle of an inert mass to insure that the housing and the jammed tool are coupled so as to be fixed with respect to rotation relative to one another when the hand-held device is deflected. An example of such a solution is found in DE-A-43 00 021. In the hand-held device described in this patent publication, a mechanical locking bar is proposed which is connected with the housing for blocking the rotary spindle by a positive engagement, with the mechanical locking bar being activated via an inert mass in the event of a sudden deflection of the hand-held device. Safety devices based on the principle of an inert mass are only activated by the jolting or jerking deflection of the housing. As a result, relatively large deflection angles can develop in hand-held devices using the safety device of this kind which acts in a purely mechanical manner.
In EP-D-0 486 843 a hand-held device is disclosed outfitted with loop spring couplings in the drive for the rotary spindle and includes a safety device cooperating with a detection device in the event the tool becomes jammed. The safety device is an additional loop spring coupling which can be electronically activated when jamming is detected and prevents rotation about a drive shaft by means of a brake spring. Accordingly, the safety device in this known hand-held device is not activated by a relatively slowly reacting inert mass. Instead, an electronic signal is generated when jamming is detected and the electronic signal causes current to be supplied to a magnet coil forming a component of an electromagnetic brake. The electromagnetic brake cooperates with a switching housing which results in a compression of the loop spring coupling and to a coupling of the drive shaft and the housing, so that they are fixed relative to one another with respect to relative rotation. This safety device is relatively complicated with respect to its construction and is designed only for hand-held devices outfitted with loop spring couplings in the drive for the rotary spindle. The loop spring is arranged at a distance from the drive shaft under normal operating conditions. When jamming occurs, this distance must be bridged for coupling the housing and the drive shaft, so that they are fixed with respect to rotation relative to one another. This feature causes a certain delay in the response of the safety device which can result in a deflection angle of the hand-held device unacceptable to the user.